To offer a functionality that could not be found in traditional rigid robots, compliant\nactuators are in development worldwide for a variety of applications and especially for humanââ?¬â??robot\ninteraction. Pneumatic bending actuators are a special kind of such actuators. Due to the absence\nof fixed mechanical axes and their soft behavior, these actuators generally possess a polycentric\nmotion ability. This can be very useful to provide an implicit self-alignment to human joint axes in\nexoskeleton-like rehabilitation devices. As a possible realization, a novel bending actuator (BA) was\ndeveloped using patented pneumatic skewed rotary elastic chambers (sREC). To analyze the actuator\nself-alignment properties, knowledge about the motion of this bending actuator type, the so-called\nskewed rotary elastic chambers bending actuator (sRECBA), is of high interest and this paper presents\nexperimental and simulation-based kinematic investigations. First, to describe actuator motion, the\nfinite helical axes (FHA) of basic actuator elements are determined using a three-dimensional (3D)\ncamera system. Afterwards, a simplified two-dimensional (2D) kinematic simulation model based\non a four-bar linkage was developed and the motion was compared to the experimental data by\ncalculating the instantaneous center of rotation (ICR). The equivalent kinematic model of the sRECBA\nwas realized using a series of four-bar linkages and the resulting ICR was analyzed in simulation.\nFinally, the FHA of the sRECBA were determined and analyzed for three different specific motions.\nThe results show that the actuatorââ?¬â?¢s FHA adapt to different motions performed and it can be assumed\nthat implicit self-alignment to the polycentric motion of the human joint axis will be provided.
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